This invention relates to a breakaway shaft assembly and, more particularly, to a vehicular steering shaft linkage having an impact absorbing apparatus as well as a breakaway apparatus effective to counter the primary impact as well as secondary impact that occurs in a collision of such vehicle.
Particularly in trucks, the steering linkage must extend from the steering wheel through a steering column assembly and through a secondary steering shaft which interconnects the steering column with the steering gear box. During a collision, the primary impact of hitting an object with the vehicle may cause the steering gear box itself to be pushed rearward toward and through the vehicle compartment. During the secondary impact, when the driver's body is thrown forward impacting the steering wheel, the normal devices used to allow the steering column itself to collapse are countered by the shifted lower steering linkage which has been moved oppositely as a result of the primary impact.
The various arrangements which have been developed for collapsing steering columns per se principally fall into two categories, one of which includes the shortening of the steering column by a telescoping movement of inner and outer tubes to absorb energy by the retraction of the column itself (see U.S. Pat. Nos. 3,877,319 and 3,262,332). Camming elements may be employed in such telescoping movement to deform one of the tubes to increase the energy absorption characteristics (see further U.S. Pat. Nos. 3,392,599; 3,461,740; 3,788,148; 3,717,046 and 3,757,601). Another is to have the column pivot about some point that permits it to move in a direction other than in axial collapse (see U.S. Pat. No. 3,923,319). Although none of the above steering column apparatus actually break away during a secondary impact, developments have been made in the art to visualize the concept of actually allowing the linkage to break at some point and become severed (see U.S. Pat. Nos. 3,600,971; 3,424,263; 4,014,219 and British Pat. No. 1,502,617).
What has not been visualized nor attained by the prior art is the construction of steering linkage which breaks away if necessary under a predetermined load upon primary impact and allows the steering linkage to additionally or alternatively collapse under the secondary impact of the driver.